1. Field of the Invention
The present invention relates to an electric power generating apparatus for a movement type equipment and a self-generation system having the same, and more particularly, to an electric power generating apparatus for a movement type equipment capable of generating electric power using vibration, periodical movement, and rotation of a movement type equipment without supply of a battery or external energy and a self-generation system having the same.
2. Description of the Background Art
Mobility of all electronic equipments will be generalized in future life. Therefore, various types of mobile power source will be developed and commonly used. In a power source of a wireless sensor, an intelligent radio frequency identification (RFID) system, and a standalone sensor, of which demand is expected to rapidly increase in a ubiquitous environment, a research has been conducted into ways of using them for long by electrically accumulating and converting a near energy source without injection of fuel or change of a battery. That is, a research has been conducted for an electric power generating apparatus for a movement type equipment that collects energy such as thermal energy and vibration energy, converts the energy into electric energy and stores them.
A generating method using a piezoelectric material has been widely used for such an electric power generating apparatus for a movement type in order to realize a simplified structure and a small size. The piezoelectric material may be defined as a material capable of mutually converting applied mechanical energy and electric energy. A piezoelectric material such as PZT and PVDF generates a voltage from applied pressure and when an electric field is applied thereto, mechanical deformation occurs. Such a piezoelectric material can convert mechanical vibration energy into electric energy, and electric energy into mechanical vibration energy, and has very high conversion efficiency. Function of the piezoelectric material is divided into a sensor and an actuator depending on its energy conversion, and the piezoelectric material is applied to a pressure sensor, a load sensor, an acceleration sensor, an actuator for precise transportation equipment, etc.
The invention, which forms the piezoelectric material in a beam shape and uses a low voltage generated when a piezoelectric beam is deformed due to external force as an energy source, is disclosed in U.S. Publication No. 20030160543 (Microelectromechanical generator using bubbles).
Meanwhile, such an electric power generating apparatus for a movement type equipment generally may be used as a power source of a tire pressure monitoring system (TPMS), e.g., as a power source of a wireless sensor mounted in a tire to measure pressure and temperature and transfer information as a signal.
The TMPS, which is one of various electronic apparatus for safe drive of vehicles, mounts a sensor in a tire to detect a temperature and pressure in the tire, and provides information for safe and economical drive to drivers. However, since electric power for operating a sensor and transferring a signal depends on only batteries, periodical change of battery is required.
In this regard, the technology that obtains electric power used for measuring pressure in a tire from a self-generating apparatus using rotation of the tire is disclosed in Japanese Laid-open Patent Publication No. 2000-214037. This technology obtains electric power from acceleration due to speed change while driving a car to rotate a magnetic rotation plate, and induces electricity from a coil installed around the rotation plate to obtain electric power necessary for driving a sensor.
In Korean Publication No. 2005-0003595 (Kim Seung-lae, et al., “self-generating apparatus for tire”) very similar to the above-mentioned invention, a structure is simplified with a method of inducing rotation by using a rotation weight symmetrically instead of a complicated rotation plate.
Also, in Korean Publication No. 2002-0059284 (power generating apparatus using load of car body applied to tire), a plurality of compartments that allows for entrance and exit of fluid are formed in a tire and a rotator is rotated using force applied to the fluid to generate power. However, processing of complicated shape is required in the tire, and energy conversion efficiency is low.
Also, in U.S. Pat. No. 6,433,465 (Energy-harvesting device using electrostrictive polymers), a multilayered piezoelectric polymer layer is used, and a voltage generated in deformation is rectified, stored, and used.
Also, in U.S. Pat. No. 7,081,693 (Energy harvesting for wireless sensor operation and data transmission), an electric circuit structure and data transmission method for a wireless communication was invented. In U.S. Pat. No. 5,801,475 (Piezo-electric generation device), a cantilever structure and a membrane structure rectifying and storing A.C. power source and controlling a generated voltage to stably generate power were invented.
However, in the case of the above-mentioned patents, only when rotation speed of a tire changes, acceleration is generated to operate a device. Also, since centrifugal force is much stronger than gravity in a constant speed movement, force is applied only in a radius direction and the device does not operate.